Process for preparing phosphine oxides and process for purifying the same

ABSTRACT

A process for preparing phosphine oxides by reacting iminophosphoranes with phosphorus oxytrichloride by which highly purified phosphine oxides can be obtained industrially in a higher yield. Specifically, phosphine oxides are prepared in such a manner that iminophosphoranes are reacted with phosphorus oxytrichloride using an aprotic organic solvent with permittivity 2.2 or more at 20° C. as a solvent under special reaction conditions to give a liquid reaction product containing phosphine oxides and aminophosphonium chlorides which are yielded as a by-product at the same time as the phosphine oxides, and the above described chlorides are removed from the above described liquid reaction product by a solid-liquid separation process, and the solution having been subjected to the solid-liquid separation process is washed with water.

This is a divisional of Application Ser. No. 09/548,624, filed Apr. 13,2000, now U.S. Pat. No. 6,303,815.

BACKGROUND OF THE INVENTION

1. Technical Field

This invention relates to a process for preparing phosphine oxideshaving the general formula (2) which comprises reactingiminophosphoranes having the general formula (1) with phosphorusoxytrichloride and to a process of purifying the above describedphosphine oxides. The present inventors previously found that the abovedescribed phosphine oxides are very effective as polymerizationcatalysts for polymerizing alkylene oxide compounds, as catalysts forproducing oxyalkylene derivatives from epoxy compounds, or as curingcatalysts for curing the raw material resin for IC sealing, and alreadyfiled an application for a patent on each of the above describedcatalysts (Japanese Patent Application No. 10-106745, Japanese PatentLaid-Open Nos. 11-302371 or 11-322901, etc.).

2. Prior Art

Except for the present inventors' patent documents, the onlypublicly-known literature on phosphine oxides having the general formula(2) is the one disclosed by G. N. Koidan et al., in Journal of GeneralChemistry of the USSR, 55, p1453 (1985).

In this literature, the compound referred to asiminotris(dimethylamino)phosphorane in this patent application, which isiminophosphorane having the general formula (1) whose R is a methylgroup, is termed hexamethyltriamidophosphazo hydride and the compoundreferred to as tris[tris(dimethylamino)phosphoranylidenamino]phosphineoxide in this patent application, which is phosphine oxide having thegeneral formula (2) whose R is a methyl group, is termedtris[tris(N,N-dimethylamido)phosphazo]phosphate.

And the compound referred to as aminotris(dimethylamino)phosphoniumchloride in this patent application, which is aminophosphonium chloridehaving the general formula (3) whose R is a methyl group, is the same asthe compound termed hexamethyltriamidophosphazo hydride hydrochlorideand shown by the form of [HN=P(NMe₂)₃].HCl in the above describedliterature. Hereinafter, for the above described three kinds ofcompounds the expressions of this application shall be used.

In the above literature, described is the reaction oftris[tris(dimethylamino)phosphoranylidenamino]phosphine oxide withmethyl iodide. And a process for preparingtris[tris(dimethylamino)phosphoranylidenamino]phosphine oxide, the rawmaterial of the above reaction, is disclosed.

The literature states thattris[tris(dimethylamino)phosphoranilidenamino]phosphine oxide wasobtained in an isolation yield of 85% by, first, adding a solution ofphosphorus oxytrichloride in petroleum ether to a solution ofiminotris(dimethylamino) phosphorane in petroleum ether drop by drop at20° C. for 30 minutes while stirring the solution mixture so that themole ratio of the above described phosphorane to phosphorusoxytrichloride becomes exactly 6:1, after that (the time is notspecified), separating the precipitate ofaminotris(dimethylamino)phosphonium chloride as a by-product, washingthe above described precipitate with petroleum ether, concentrating thefiltrate, followed by crystallizing the residue from a small amount ofthe petroleum ether.

However, when the present inventors carried out the preparation oftris(tris(dimethylamino)phosphoranilidenamino phosphine oxide under thesame conditions as above, even after the addition of phosphorusoxytrichloride at 20° C. for 30 minutes, almost no object compound wasproduced, as shown in comparative example 5 below. After that, thereaction was proceeded at a raised temperature of 40° C. for 24 hours,however, the reaction yield of the object compound was as low as about60%. Even after an additional 48 hours of reaction, the reaction yieldwas about 73% at the most.

In addition, the above literature only states thattris[tris(dimethylamino)phosphoranylidenamino]phosphine oxide wasobtained “by crystallizing the residue from a small amount of thepetroleum ether”, but does not describe in detail the recrystallizationprocess. The present inventors attempted recrystallization of crudephosphine oxide in such a manner that, first precipitate was separatedby filtration from the liquid reaction product obtained after the 48hours' reaction at 40° C., as described above, then the filtrate wasconcentrated to dry to become a solid.

As shown in comparative example 6 below, a small amount of crystaldeposition was observed only after the filtrate was cooled to −10° C.,and the crystal could be finally gathered after the filtrate was cooledto an extremely low temperature of −20° C. The isolation yield of thecrystal, that is, the isolation yield oftris[tris(dimethylamino)phosphoranylidenamino]phosphine oxide was as lowas 20%, and moreover, the crystal contained a large amount of chlorineion (about 600 ppm). Such residue of chlorine ion is a very seriousproblem when the above described phosphine oxide is used as a curingcatalyst for curing the raw material resin for IC sealing which isrequired to have an electrical insulating property.

In the case wheretris[tris(dimethylamino)phosphoranylidenamino]phosphine oxide isprepared by reacting iminotris(dimethylamino) phosphorane withphosphorus oxytrichloride, if one molecule of iminotris(dimethylamino)phosphorane reacts with one molecule of phosphorus oxytrichloride, onemolecule of hydrogen chloride is yield at the same time. This hydrogenchloride immediately reacts with iminotris(dimethylamino) phosphorane toyield ionic aminotris(dimethylamino)phosphonium chloride. Accordingly, 6moles of iminotris(dimethylamino) phosphorane is requiredstoichiometrically so as to react all of the three chlorines of one moleof phosphorus oxytrichloride. This is expressed by the followingreaction equation.

6HN═P(NMe₂)₃+O═PCl₃→O═P[N═P(NMe₂)₃]₃+3[H₂N—P⁺(NMe₂)₃]Cl⁻

As shown in comparative example 7 below, in the purifying processdescribed in the above described literature, when imino(dimethylamino)phosphorane was used in excess of that stoichiometrically required so asto increase yields, the unreacted residue of the above describedphosphorane could not be removed sufficiently, which led to a decreasein purity of recrystallizedtris[tris(dimethylamino)phosphoranylidenamino]phosphine oxide.

Thus, the above disclosed process for preparing:tris[tris(dimethylamino)phosphoranylidenamino]phosphine oxide is stillvery insufficient as an industrial process in that: its reaction andisolation yields are low, the purification process for its productrequires an extremely low temperature, the ionic compound yielded by itsreaction cannot be removed sufficiently, and its unreacted raw materialcannot be removed sufficiently when using one reactant in excess of thatstoichiometrically required in order to increase yields.

SUMMARY OF THE INVENTION

Accordingly, it is a primary object of the present invention to providea process for preparing phosphine oxides having the general formula (2)in a raised yield which comprises reacting iminophosphoranes having thegeneral formula (1) with phosphorus oxytrichloride.

Another object of the present invention is to provide a process forpurifying the above described phosphine oxides which makes it possiblein an industrially more realistic manner to remove unreacted rawmaterials and ionic impurities in a liquid reaction product and toprovide a high yield and purity of the above described phosphine oxides.

After continuously concentrating their energies on investigatingprocesses for preparing and purifying the above described phosphineoxides so as to achieve the above objects, the present inventors finallyfound that in the process for preparing phosphine oxides having thegeneral formula (2) which comprises reacting iminophosphoranes havingthe general formula (1) with phosphorus oxytrichloride, the use of anaprotic organic solvent with permittivity 2.2 or more at 20° C. insteadof petroleum ether (with permittivity 1.85 to 1.95 at 20° C.), as areaction solvent, increases the reaction rate remarkably and gives theabove described phosphine oxides in a high yield.

In addition, it was found that, although one part by weight of petroleumether is a good solvent to dissolve 1.5 parts by weight or more of theabove described phosphine oxides, when the liquid reaction productreacted in a petroleum ether as a reaction solvent is washed with asmall amount of water, almost all amount of the above describedphosphine oxides moves to a water phase and there is almost none left ina petroleum ether phase.

Surprisingly, however, it was found that in a liquid reaction productobtained by using a specific solvent, such as o-dichlorobenzene, almostall amount of the above described phosphine oxides is left in an organicphase even after water-washing and almost all amount of theaminophosphonium chlorides having the general formula (3) which areyielded by the reaction and the unknown compounds as by-products move toa water phase, as shown in example 8 below. Further surprisingly, it wasalso found that, when iminophosphoranes are used in a stoichiometricallyrequired amount or in excess of the same amount, almost all amount ofthe iminophosphoranes having the general formula (1) which are leftunreacted in the liquid reaction product move to a water phase.

As described above, the present inventors found that the use of anaprotic organic solvent with permittivity 2.2 or more at 20° C. as areaction solvent is effective in increasing the reaction rate as well asthe reaction yield, as a result, producing the phosphine oxides havingthe general formula (2) in a high yield, and in increasing the purity ofthe above described phosphine oxides simply by water-washing thesolution containing the above described phosphine oxides and a specificorganic solvent while keeping the isolation yield almost the same. Thusthe present invention was completed.

Accordingly, the first aspect of the present invention is a process forpreparing phosphine oxides having the following general formula (2):

wherein R represents the same kind or different kinds of hydrocarbongroup(s) with 1 to 10 carbon atom(s), and two Rs on the same nitrogenatom can combine with each other to form a ring structure, whichcomprises reacting iminophosphoranes having the following generalformula (1):

wherein R is the same as that of the formula (2), with phosphorusoxytrichloride, in the presence of an aprotic organic solvent withpermittivity 2.2 or more at 20° C. as a reaction solvent.

The second aspect of the present invention is a process for purifyingphosphine oxides which comprises water-washing a solution containing atleast phosphine oxides having the general formula (2) and an organicsolvent which does not substantially mix with water to give the abovedescribed phosphine oxides as a solution, or concentrating to dry theabove described solution to give the above described phosphine oxides asa solid.

DETAILED DESCRIPTION OF THE INVENTION

In the preparation and purification processes of the present invention,the chemical structure of phosphine oxides is expressed by the generalformula (2); however, the formula just expresses one canonicalstructure. According to the formula (2), a double bond is formed betweenphosphorus atom and oxygen atom; however, phosphine oxides may haveanother canonical structure where electrons cluster on the side ofoxygen atom to form an anion of oxygen and a cation of phosphorus(P⁺—O⁻). The cation of phosphorus may be delocalized through aconjugated system. It should be understood that phosphine oxides havingthe formula (2) in the preparation and purification processes of thepresent invention are resonance hybrids including all of the abovedescribed structure.

In the preparation and purification processes of the present invention,R of iminophosphoranes having the general formula (1), of phosphineoxides having the formula (2) and of aminophosphonium chlorides havingthe formula (3) represents the same kind of or different kinds ofhydrocarbon group(s) with 1 to 10 carbon atom(s). In particular, the Rrepresents an aliphatic or aromatic hydrocarbon group such as methyl,ethyl, n-propyl, isopropyl, allyl, n-butyl, sec-butyl, tert-butyl,2-butenyl, 1-pentyl, 2-pentyl, 3-pentyl, 2-methyl-1-butyl, isopentyl,tert-pentyl, 3-methyl-2-butyl, neopentyl, n-hexyl, 4-methyl-2-pentyl,cyclopentyl, cyclohexyl, 1-heptyl, 3-heptyl, 1-octyl, 2-octyl,2-ethyl-1-hexyl, 1,1-dimethyl-3,3-dimethylbutyl (commonly known astert-octyl), nonyl, decyl, phenyl, 4-toluyl, benzyl, 1-phenylethyl, or2-phenylethyl.

When two Rs on the same nitrogen atom of iminophosphoranes having thegeneral formula (1), of phosphine oxides having the formula (2) and ofaminophosphonium chlorides having the formula (3) combine with eachother to form a ring structure together with the nitrogen atom, theformed cyclic amino groups are cyclic secondary amino groups containing4 to 6 carbon atoms on the ring, and —NR₂'s are cyclic secondary aminogroups of 5 to 7 members including a nitrogen atom.

The above described cyclic secondary amino groups include, for example,pyrrolidine-1-yl group, piperidine-1-yl group, morpholine-4-yl group,and substitution products thereof substituted with alkyl groups such asmethyl group and ethyl group.

All of or part of the potential nitrogen atoms of the above describediminophosphoranes, phosphine oxides and aminophosphonium may participatein the formation of such a ring structure.

R is preferably an aliphatic hydrocarbon group with 1 to 8 carbon atoms,such as methyl, ethyl, n-propyl, isopropyl, tert-butyl, tert-pentyl, or1,1-dimethyl-3,3-dimethylbutyl, and more preferably a methyl group.

The above described iminophosphoranes having the general formula (1) canbe synthesized in the same manner as the description in EP-0921128 or G.N. Koidan et al., Zh. Obshch. Khim., 50, 679-680 (1980). Of the abovedescribed iminophosphoranes, the one whose R is a methyl group iscommercially available.

The first aspect of the present invention is a process for preparingphosphine oxides having the formula (2) which comprises reactingiminophosphoranes having the general formula (1) with phosphorusoxytrichloride, wherein an aprotic organic solvent with permittivity 2.2or more at 20° C. is used as a reaction solvent.

The preparation process of the present invention is characterized by useof an aprotic organic solvent with permittivity 2.2 or more at 20° C. asa reaction solvent. The use of an aprotic organic solvent withpermittivity less than 2.2 at 20° C. as a reaction solvent causes anextreme decrease in reaction rate under the same mild conditions. On theother hand, if the reaction temperature is raised so as to increase thereaction rate, a side reaction proceeds, as a result of which phosphineoxides having the general formula (2) cannot be obtained in a highyield.

The aprotic organic solvents with permittivity less than 2.2 at 20° C.include, for example, petroleum ether (1.85 to 1.95; permittivity at 20°C. and so on), hexane (1.89), decane (1.99), 1-hexene(2.06), 1-octene(2.08), cyclohexane (2.05) and decalin (2.19), all of which are notpreferable as a reaction solvent of the present invention.

Concrete examples of the aprotic organic solvents with permittivity 2.2or more at 20° C. used in the preparation process of the presentinvention as a reaction solvent include, for example, halogenatedaliphatic hydrocarbons such as methylene chloride, chloroform,1,2-dichloroethane, 1,1-dichloroethane or hexachloroethane; aromatichydrocarbons such as benzene, toluene, o-xylene, m-xylene, p-xylene,mixed xylene, ethylbenzene, normal propylbenzene, cumene,1,2,3-trimethylbenzene, 1,2,4-trimethylbenzene, mesitylene, tetralin,butylbenzene, p-cymene, cyclohexylbenzene, 1,4-diethylbenzene,1,3-diisopropylbenzene or dodecylbenzene; halogenated aromatichydrocarbons such as chlorobenzene, o-dichlorobenzene,m-dichlorobenzene, bromobenzene, o-dibromobenzene,1-bromo-2-chlorobenzene, 1-bromonaphthalene, 1-chloronaphthalene,2-chlorotoluene, 2-bromotoluene, 2,4-dichlorotoluene,1-bromo-2-ethylbenzene, 2-chloro-o-xylene or 1,2,4-trichlorobenzene;ethers such as diethyl ether, dipropyl ether, diisopropyl ether, dibutylether, dimethoxyethane, diethylene glycol dimethyl ether,tetrahydrofuran, tetrahydropyran, 1,4-dioxane, anisole or phenetol;esters such as methyl formate, ethyl formate, propyl formate, isobutylformate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate,methyl propionate, ethyl propionate, methyl butyrate, methyl benzoate,isopentyl benzoate or ethyl cinnamate; nitro compounds such asnitromethane, nitroethane or nitrobenzene; and polar compounds such asacetonitrile, propionitrile, benzonitrile, N,N-dimethylformamide,N-methylpyrrolidone, dimethyl sulfoxide or hexamethylphosphorictriamide.For further details, refer to Teruzo Asahara et al. Handbook of Solvents(Tokyo: Kodansha Publishing Company, 1982).

Any other aprotic organic solvents may be used, as long as theirpermittivity is 2.2 or more at 20° C. and they do not hinder thepreparation process of the present invention. These aprotic organicsolvents may be used independently or jointly. Further, the aproticorganic solvent system which is a mixture of the above described aproticorganic solvents and the aprotic organic solvents with permittivity lessthan 2.2 at 20° C. and allowed to have permittivity of 2.2 or more at20° C. should be understood as an “aprotic organic solvent withpermittivity 2.2 or more at 20° C.” in the preparing process of thepresent invention.

Of these aprotic organic solvents, preferable are those which do notdissolve aminophosphonium chlorides having the formula (3) describedbelow. The preferable aprotic organic solvents include, for example,aromatic hydrocarbons such as benzene, toluene, o-xylene, m-xylene,p-xylene, mixed xylene, ethylbenzene, normal propylbenzene, cumene,1,2,3-trimethylbenzene, 1,2,4-trimethylbenzene, mesitylene, tetralin,butylbenzene, p-cymene, cyclohexylbenzene, 1,4-diethylbenzene,1,3-diisopropylbenzene or dodecylbenzene; halogenated aromatichydrocarbons such as chlorobenzene, o-dichlorobenzene,m-dichlorobenzene, bromobenzene, o-dibromobenzene,1-bromo-2-chlorobenzene, 1-bromonaphthalene, 1-chloronaphthalene,2-chlorotoluene, 2-bromotoluene, 2,4-dichlorotoluene,1-bromo-2-ethylbenzene, 2-chloro-o-xylene or 1,2,4-trichlorobenzene; andethers such as diethyl ether, dipropyl ether, diisopropyl ether, dibutylether, dimethoxyethane, diethylene glycol dimethyl ether,tetrahydrofuran, tetrahydropyran, 1,4-dioxane, anisole or phenetol.

Of the above described aprotic organic solvents, more preferable arethose substantially immiscible with water as described in thepurification process of the present invention. The aprotic organicsolvents substantially immiscible with water include, for example,aromatic hydrocarbons such as benzene, toluene, o-xylene, m-xylene,p-xylene, mixed xylene, ethylbenzene, normal propylbenzene, cumene,1,2,3-trimethylbenzene, 1,2,4-trimethylbenzene, mesitylene, tetralin,butylbenzene, p-cymene, cyclohexylbenzene, 1,4-diethylbenzene,1,3-diisopropylbenzene or dodecylbenzene; and halogenated aromatichydrocarbons such as chlorobenzene, o-dichlorobenzene,m-dichlorobenzene, bromobenzene, o-dibromobenzene,1-bromo-2-chlorobenzene, 1-bromonaphthalene, 1-chloronaphthalene,2-chlorotoluene, 2-bromotoluene, 2,4-dichlorotoluene,1-bromo-2-ethylbenzene, 2-chloro-o-xylene or 1,2,4-trichlorobenzene. Andmore preferable are toluene, chlorobenzene, dichlorobenzene or2,4-dichlorotoluene.

The amount of these aprotic organic solvents used is not expresslyrestricted; however, it is normally 500 weight parts or less per 1weight part of phosphorus oxytrichloride as a raw material, preferably 1to 100 weight parts, and more preferably 1.5 to 50 weight parts. It isnot a problem that part of the liquid phosphorus oxytrichloride can beimmiscible with these aprotic organic solvents.

In the preparation process of the present invention, the mole ratio ofiminophosphoranes having the formula (1) used to phosphorusoxytrichloride is not expressly restricted; however, it is normally 5 to12, preferably 6 to 10, and more preferably 6.1 to 8.0.

The reaction temperature varies depending on the amount of solvent used,on the mole ratio of the raw materials, etc.; however, it is normally−10 to 200° C., preferably 0 to 150° C., and more preferably 15 to 100°C. In the reaction, the set temperature may be changed phase by phase;for example, the reaction may be carried out at a relatively lowtemperature in the beginning and at a relatively high temperature in thelast.

The reaction may be carried out under reduced pressure, under normalpressure and under pressure; however, it is normally carried out undernormal pressure. The reaction time varies depending on the reactiontemperature and other factors; however, it is normally 0.1 to 100 hours,preferably 0.5 to 50 hours, and more preferably 1 to 30 hours.

In the liquid reaction product thus obtained, aminophosphonium chlorideshaving the formula (3) can sometimes be deposited as a solid and cansometimes be dissolved depending on the kind or amount of the solventused or on the kind of iminophosphoranes having the formula (1). Themethods of removing the above described phosphonium chlorides in suchstates are not restricted to specific ones and any methods can be usedto remove them; however, when the above described phosphonium chloridesare deposited in the liquid reaction product as a solid, the method inwhich the liquid reaction product directly undergoes a solid-liquidseparation is normally used; and when the above described phosphoniumchlorides are dissolved in the liquid reaction product, first thesolvent used is distilled from the liquid, then another organic solventwhich does not dissolve the above described phosphonium chlorides isadded, and the liquid reaction product can undergo a solid-liquidseparation.

The above solid-liquid separation can be conducted using any methods;however, general-purpose methods such as filtration, centrifugation anddecantation are normally used. Of the above methods, filtration is mostpreferable. If needed, filter cake can be washed with the abovedescribed aprotic organic solvent or an organic solvent which does notdissolve the above described phosphonium chlorides, and the washings maybe added to the filtrate.

The organic solvents which do not dissolve the above describedphosphonium chlorides include, for example, saturated aliphatichydrocarbons such as normal pentane, normal hexane, 2,2-dimethylbutane,2,3-dimethylbutane, 2-methylpentane, normal heptane, normal octane,2,3,3-trimethylpentane, isooctane, normal nonane, 2,2,5-trimethylhexaneor normal decane; alicyclic hydrocarbons such as cyclopentane,methylcyclopentane, cyclohexane, methylcyclohexane, ethylcyclohexane,p-menthane, bicyclohexyl or decalin; aromatic hydrocarbons such as.benzene, toluene, o-xylene, m-xylene, p-xylene, mixed xylene,ethylbenzene, normal propylbenzene, cumene, 1,2,3-trimethylbenzene,1,2,4-trimethylbenzene, mesitylene, tetralin, butylbenzene, p-cymenelcyclohexylbenzene, 1,4-diethylbenzene, 1,3-diisopropylbenzene ordodecylbenzene; halogenated aromatic hydrocarbons such as chlorobenzene,o-dichlorobenzene, m-dichlorobenzene, bromobenzene, o-dibromobenzene,1-bromo-2-chlorobenzene, 1-bromonaphthalene, 1-chloronaphthalene,2-chlorotoluene, 2-bromotoluene, 2,4-dichlorotoluene,1-bromo-2-ethylbenzene, 2-chloro-o-xylene or 1,2,4-trichlorobenzene; andethers such as diethyl ether, dipropyl ether, diisopropyl ether, dibutylether, dimethoxyethane, diethylene glycol dimethyl ether,tetrahydrofuran, tetrahydropyran, 1,4-dioxane, anisole or phenetol. Theorganic solvents which do not dissolve the above described phosphoniumchlorides are, however, limited to the above described ones.

The above described phosphonium chlorides separated as solids can bere-formed as iminophosphoranes having the formula (1) by the methoddescribed in EP-0921128 or G. N. Koidan et al., Zh. Obshch. Khim., 50,679-680 (1980) and recycled as part or the whole of theiminophosphoranes having the formula (1) in the preparation process ofthe present invention.

In the mother liquor from which the aminophosphonium chlorides havingthe formula (3) have been removed, there exist iminophosphoranes havingthe formula (1) which remain unreacted or are added in excess. Themethods of removing the above described phosphoranes are not restrictedto specific ones and any methods can be used to remove them; however,normally used are the method in which the above described mother liquoris concentrated to dry and the above described phosphoranes aredistilled off under normal pressure or under reduced pressure and themethod in which the above described mother liquor is washed with wateras described below.

The dried solid and the solution having undergone water washing thusobtained contain phosphine oxides having the formula (2) of asufficiently high purity. Although they can sometimes be used as theyare for next purpose, they can sometimes be used as a concentratedsolution or a solid by removing a small amount of water containedtherein with a drying agent or by distillation or, in case of solutionshaving undergone the above described water washing, by removing part ofor the whole solvent used.

The second aspect of the present invention is a process for purifyingphosphine oxides having the formula (2) which comprises water washing asolution containing at least the above described phosphine oxides and anorganic solvent substantially immiscible with water to give the abovedescribed phosphine oxides as a solution, or further comprisesconcentrating to dry the above described solution to give the abovedescribed phosphine oxides as a solid.

“The organic solvents substantially immiscible with water” used in thepurification process of the present invention mean organic solventsconventionally used for extraction etc. which dissolve in water toolittle to be taken into consideration and can be easily separated fromwater phase. In addition, the partition rate of their phase to waterphase is high in terms of phosphine oxides having the formula (2), andthey cause no chemical process even if they come in contact with theabove described phosphine oxides. The organic solvents substantiallyimmiscible with water as described above include, for example,halogenated aliphatic hydrocarbons such as methylene chloride,chloroform, 1,2-dichloroethane, 1,1-dichloroethane or hexachloroethane;aromatic hydrocarbons such as benzene, toluene, o-xylene, m-xylene,p-xylene, mixed xylene, ethylbenzene, normal propylbenzene, cumene, 1,2,3-trimethylbenzene, 1,2,4-trimethylbenzene, mesitylene, tetralin,butylbenzene, p-cymene, cyclohexylbenzene, 1,4-diethylbenzene,1,3-diisopropylbenzene or dodecylbenzene; halogenated aromatichydrocarbons such as chlorobenzene, o-dichlorobenzene,m-dichlorobenzene, bromobenzene, o-dibromobenzene,1-bromo-2-chlorobenzene, 1-bromonaphthalene, 1-chloronaphthalene,2-chlorotoluene, 2-bromotoluene, 2,4-dichlorotoluene,1-bromo-2-ethylbenzene, 2-chloro-o-xylene or 1,2,4-trichlorobenzene; andesters having 4 or more of carbon atoms such as propyl formate, isobutylformate, ethyl acetate, propyl acetate, butyl acetate, methylpropionate, ethyl propionate, methyl butylate, methyl benzoate,isopentyl benzoate or ethyl cinnamate. Any other organic solvents may beused, as long as they do not hinder the purification process of thepresent invention.

Of the above described organic solvents, preferable are aprotic organicsolvents with permittivity 2.2 or more at 20° C. which do not dissolveaminophosphonium chlorides having the formula (3). The preferableaprotic organic solvents include, for example, aromatic hydrocarbonssuch as benzene, toluene, o-xylene, m-xylene, p-xylene, mixed xylene,ethylbenzene, normal propylbenzene, cumene, 1,2,3-trimethylbenzene,1,2,4-trimethylbenzene, mesitylene, tetralin, butylbenzene, p-cymene,cyclohexylbenzene, 1,4-diethylbenzene, 1,3-diisopropylbenzene ordodecylbenzene; and halogenated aromatic hydrocarbons such aschlorobenzene, o-dichlorobenzene, m-dichlorobenzene, bromobenzene,o-dibromobenzene, 1-bromo-2-chlorobenzene, 1-bromonaphthalene,1-chloronaphthalene, 2-chlorotoluene, 2-bromotoluene,2,4-dichlorotoluene, 1-bromo-2-ethylbenzene, 2-chloro-o-xylene or1,2,4-trichlorobenzene. More preferable are toluene, chlorobenzene oro-dichlorobenzene.

“A solution containing at least phosphine oxides having the formula (2)and an organic solvent substantially immiscible with water” used in thepurification process of the present invention means a solutioncontaining at least the above described two components, and there mayexist other components in the solution, as long as they do not hinderthe purification process of the present invention. Further, the solutionmay be a solution formed by dissolving the above described phosphineoxides, which was once separated from another solution, in an organicsolvent substantially immiscible with water.

Further, the solution may be a solution formed by removing solidaminophosphonium chlorides having the formula (3) from a liquid reactionproduct containing phosphine oxides having the formula (2) and the abovedescribed aminophosphonium chlorides by the solid-liquid separationprocess, wherein the liquid reaction product is formed by reactingiminophosphoranes having the formula (1) with phosphorus oxytrichlorideusing as a reaction solvent an aprotic organic solvent with permittivity2.2 or more at 20° C. which is substantially immiscible with water anddoes not dissolve the aminophosphonium chlorides having the formula (3),the above descried phosphine oxides and phosphonium chlorides beingyielded at the same time by the above described reaction. According tothe situations, the solution may be a solution formed in such a mannerthat, first the above described reaction is carried out using an aproticorganic solvent with permittivity 2.2 or more at 20° C. as a reactionsolvent, then the above described solvent is removed by, for example,the method of distilling solvent from the solution obtained by thesolid-liquid separation process, which is described in the preparationprocess of the present invention, finally another desired organicsolvent substantially immiscible with water is added instead of theabove described solvent removed.

Of the above described solutions, preferable is a solution formed byremoving solid aminophosphonium chlorides having the formula (3) from aliquid reaction product containing phosphine oxides having the formula(2) and the above described aminophosphonium chlorides by thesolid-liquid separation process, wherein the liquid reaction product isformed by reacting iminophosphoranes having the formula (1) withphosphorus oxytrichloride using as a reaction solvent an aprotic organicsolvent with permittivity 2.2 or more at 20° C. which is substantiallyimmiscible with water and does not dissolve the aminophosphoniumchlorides having the formula (3), the above descried phosphine oxidesand phosphonium chlorides being yielded at the same time by the abovedescribed reaction. And more preferable is a solution formed by removingthe above described phosphonium chlorides from a liquid reaction productcontaining the same by the solid-liquid separation process, wherein theliquid reaction product is formed by reacting the above describedphosphoranes with phosphorus oxytrichloride at the above describedphosphoranes to phosphorus oxytrichloride mole ratio within 6 to 10.

As a method of water washing in the purification process of the presentinvention, any method can be used as long as the method allows thesolution containing at least phosphine oxides having the formula (2) andan organic solvent substantially immiscible with water and water tosufficiently come in contact with each other. Usually water washing canbe carried out in such a manner that first water is added to the abovedescribed solution, the solution is fully stirred, and its water phaseis removed after its organic phase and water phase are separated fromeach other.

The amount of water used for the water washing is not expresslyrestricted; however, 5 weight parts or less of water is usually used per1 weight part of the above described solution. The water washing can becarried out using such an amount of water in several installments.Preferably the water washing is carried out 2 to 5 times using 0.05 to1.0 weight parts of water at a time per 1 weight part of the abovedescribed solution. The temperature and duration of water washing arenot expressly restricted; however, the temperature is usually 10 to 80°C., preferably 15 to 40° C., and the duration is usually within 3 hours,preferably 0.01 to 1 hour, more preferably 0.05 to 0.5 hours.

A solution of phosphine oxides having the formula (2) which has beensubjected to water washing in the above manner contains the abovedescribed phosphine oxides of a higher purity, and it can sometimes beused as it is for the next purpose. The above described phosphine oxidescan be obtained as solids by concentrating to dry the solution.

According to situations, the dried solids can be further purified. Thesolvent used may be completely removed from the dried solids, or it mayremain in the solids in a small amount. There exist a trace ofimpurities left dissolved in such solids even after water washing. Themethods of further purifying such solids are not expressly restricted;however, a method in which one of hydrocarbons is added to the driedsolids so as to dissolve phosphine oxides having the formula (2) and atrace of solids (impurities) left undissolved are removed by thesolid-liquid separation process is preferable, effective and practical.

Hydrocarbons used in this method include, for example, saturatedaliphatic hydrocarbons such as normal pentane, normal hexane,2,2-dimethylbutane, 2,3-dimethylbutane, 2-methylpentane, normal heptane,normal octane, 2,3,3-trimethylpentane, isooctane, normal nonane,2,2,5-trimethylhexane or normal decane; alicyclic hydrocarbons such ascyclopentane, methylcyclopentane, cyclohexane, methylcyclohexane,ethylcyclohexane, p-menthane, bicyclohexyl or decalin; and aromatichydrocarbons such as benzene, toluene, o-xylene, m-xylene or p-xylene.

Any other hydrocarbons may be used as long as they do not hinder thismethod. These hydrocarbons may be used independently or jointly. Of theabove described hydrocarbons, preferable are saturated aliphatichydrocarbons having 5 to 10 carbon atoms, such as normal pentane, normalhexane, normal heptane, normal octane, normal nonane or normal decane.

The amount of these hydrocarbons used is not expressly restricted;however, usually used are hydrocarbons 0.5 to 50 times as heavy as theabove described dried solids, preferably hydrocarbons 1 to 20 times asheavy as the above described dried solids. When hydrocarbons are addedto the above described dried solid to dissolve phosphine oxides havingthe formula (2), the temperature and duration in the above operation arenot expressly restricted; however, the temperature is usually 10 to 100°C., preferably 20 to 50° C., the duration is usually 0.1 to 3 hours,preferably 0.5 to 2 hours. After that, the solid left undissolved in theabove described hydrocarbon solution is removed by the solid-liquidseparation process. The solid-liquid separation can be conducted usingany methods; however, general-purpose methods such as filtration,centrifugation and decantation are usually used. Of the above methods,filtration is most preferable. The undissolved solid can be washed withhydrocarbons, and the washings may be combined to the filtrate.

Thus, a solution containing phosphine oxides having the formula (2) of aextremely high purity can be obtained. If needed, the above describedsolution can be concentrated to dry to obtain the above describedphosphine oxides as a solid.

The present invention will be further illustrated by the followingexamples; however, these examples are intended to illustrate theinvention and are not intended to limit the invention to the specificexamples.

EXAMPLE 1

Under a nitrogen atmosphere, 54.3 g (305 mmol) ofiminotris(dimethylamino) phosphorane, which is iminophosphorane havingthe formula (1) whose R is a methyl group, and 130 g of driedo-dichlorobenzene (with permittivity 6.80 at 20° C.) were prepared in a300 ml glass reactor vessel. Then, a liquid mixture of 7.67 g (50.0mmol) of phosphorus oxytrichloride and 16.3 g of dried o-dichlorobenzene(the concentration of phosphorus oxytrichloride was 32 weight %) wasadded drop by drop over 30 minutes while stirring the mixture andcontrolling the internal temperature to be kept at 20° C. The mole ratioof iminotris(dimethylamino)phosphorane to phosphorus oxytrichloride was6.1. At this time, part of the liquid reaction product was taken as asample.

A ³¹P-NMR quantitative analysis was conducted using dimethyl sulfoxidedeuteride as a solvent and tri-normal-butyl phosphate as an internalstandard compound (hereafter, yield and purity were analyzed in thismanner). The analysis shows that almost notris[tris(dimethylamino)phosphoranylidenamino]phosphine oxide, which isphosphine oxide having the formula (2) whose R is a methyl group, wasformed. Then, the temperature of the liquid reaction product was raisedto 40° C. and the reaction was continued for 24 hours, as a result ofwhich the above described phosphine oxide was obtained in a reactionyield to phosphorus oxytrichloride of 83.6%.

This result, together with the results of examples 2 to 7 andcomparative examples 1 to 4 where reaction was carried out usingrespective solvents other than o-dichlorobenzene whose permittivity is2.2 or more or less than 2.2 at 20° C., is shown in Table 1. Table 1shows that there existed a big clear difference in reaction rate betweenthe solvents with permittivity 2.2 or more at 20° C. and withpermittivity less than 2.2 at 20° C., in addition, the use of thesolvents with permittivity 2.2 or more at 20° C. is very effective inincreasing the reaction yield of the object compound.

EXAMPLES 2-7 Comparative Examples 1-4

The reaction was carried out exactly in the same manner as example 1,except that various types aprotic organic solvents shown in Table 1 wereused instead of o-dichlorobenzene.

TABLE 1 Aprotic Organic Permittivit Reaction Examples Solvent y Yield(%) Example 2 Benzene 2.28 81.9 Example 3 Chloroform 4.81 81.3 Example 4Ethyl Acetate 6.08 85.4 Example 1 o- 6.80 83.6 Dichlorobenzene Example 5Tetrahydrofuran 7.60 89.7 Example 6 Nitrobenzene 34.9 92.2 Example 7Acetonitrile 37.5 91.6 Comparati Hexane 1.89 55.6 ve Example 1 ComparatiPetroleum Ether 1.85-1.95 58.1 ve Example 2 Comparati 1-Hexene 2.06 57.5ve Example 3 Comparati Decalin 2.19 51.9 ve Example 4 Note: Permittivityrepresents permittivity at 20° C.

EXAMPLE 8

Under a nitrogen atmosphere, 15.4 g (100 mmol) of phosphorusoxytrichloride and 154 g of dried o-dichlorobenzene were prepared in a500 ml glass reactor vessel. Then, 116 g (651 mmol) ofiminotris(dimethylamino) phosphorane was added drop by drop over 1 hourwhile stirring the mixture and controlling the bulk temperature to bekept at 70° C. or lower. The mole ratio ofiminotris(dimethylamino)phosphorane to phosphorus oxytrichloride was6.5. After completing the addition ofiminotris(dimethylamino)phosphorane, stirring was continued at 70° C.for 1 hour, so as to obtain a white slurry. Part of this liquid reactionproduct was taken as a sample and a quantitative analysis was conducted.The analysis shows that the reaction yield oftris[tris(dimethylamino)phosphoranylidenamino]phosphine, oxide was85.4%.

After the reaction, the above described white slurry was filtered, thesolid was washed with a small amount of o-dichlorobenzene, and 266 g offiltrate and washings was obtained. The filtrate and washings was takenin a 300 ml separating funnel, 31.9 g of water (0.12 times as heavy asthe filtrate and washings) was added, and water-washing was conducted ofthe filtrate and washings while intensely shaking the separating funnelso that both of the o-dichlorobenzene phase and the water phase weresatisfactorily contacted with each other,- then the separating funnelwas allowed to stand still to separate the o-dichlorobenzene phase andthe water phase from each other, and each phase was collected as asample. This water-washing operation was carried out another two times.

A quantitative analysis was conducted of the o-dichlorobenzene phaseobtained, and the analysis shows thatiminotris(dimethylamino)phosphorane, which was left unreacted beforewater-washing, was decreased to an amount less than the limit ofdetection and the amount of by-products was also drastically decreasedcompared with that before water-washing. Then, the o-dichlorobenzenephase was concentrated to dry at 80° C., 10 mmHg to obtain 50.5 g ofwhite solid.

The purity of tris[tris(dimethylamino)phosphoranylidenamino]phosphineoxide in the solid was 95.4 weight % and the isolation yield was 83.3%.As described above,.the above described phosphine oxide was obtainedwith little loss and with a satisfactorily high purity only bywater-washing the filtrate and washings after filtrating the liquidreaction product.

In order to further purify the above described phosphine oxide, theobtained solid was dissolved in normal hexane which was 10 times asheavy as the solid while stirring the solution over 40 minutes. Afterthat, the solid left undissolved was filtered, and the undissolvedmatter was washed with a small amount of normal hexane. The undissolvedsolid was about 1.9 g in weight after being dried. The filtrate andwashings obtained was concentrated to dry at 60° C., 10 mmHG andsubjected to drying operation at 80° C. for 5 hours under the flow ofnitrogen.

As a result, 48.5 g of white solid was obtained, and its isolation yieldwas 83.1% and its purity was increased to as high as 99.2 weight %.Then, the chlorine ion content of the solid was measured by thepotentiometric titration method using a chlorine ion electrode(hereafter the same as above). The measured value was 43 ppm.

Comparative Example 5

The reaction was carried out in accordance with the process described inthe literature by G. N. Koidan et al.

Under a nitrogen atmosphere, 53.5 g (300 mmol) ofiminotris(dimethylamino) phosphorane and 200 ml of dried petroleum etherwere prepared in a 300 ml glass reactor vessel (the concentration of theabove described phosphorane was 29 weight %). Then, a liquid mixture of7.67 g (50.0 mmol) of phosphorus oxytrichloride and 25 ml of driedpetroleum ether (the concentration of phosphorus oxytrichloride was 32weight %) was added drop by drop over 30 minutes while stirring themixture and controlling the bulk temperature to be kept at 20° C.

The mole ratio of iminotris(dimethylamino)phosphorane to phosphorusoxytrichloride was 6.0. At this time, part of the liquid reactionproduct was taken as a sample, and it was found that almost no objectcompound was formed. Then, the liquid reaction product was heated at itsreflux temperature. (about 40° C.) and the reaction was continued. Theyields after 24 hours and 48 hours were 59.8% and 73.0%, respectively.As is apparent when compared with the results of examples 1 to 7, in theprocess in accordance with the description in the above describedliterature, both reaction rate and yield were low.

Comparative Example 6

Purification was carried out using the liquid reaction product obtainedin accordance with the process described in the literature by G. N.Koidan et al. (the liquid reaction product obtained in comparativeexample 5) in accordance with the purification process described in theabove described literature.

The white slurry of petroleum ether obtained from the reaction incomparative example 5 was filtered, the solid left after the filtrationwas washed twice with 50 ml of petroleum ether, and the obtainedfiltrate and washings was concentrated to dry at 30° C., 150 mmHg. As aresult, 21.5 g of faintly yellowish white solid was obtained. When 6.0 gof petroleum ether (only 28 weight % of the solid) was added, the solidwas almost completely dissolved in the petroleum ether at 25° C. Thesolution thus obtained was filtered, and the filtrate was cooled so asto crystallize. However, a very small amount of crystallization wasobserved only after the temperature of the filtrate was reduced to −10°C.

The filtrate temperature was further reduced to −20° C., and a certainamount of crystallization was finally achieved. The filtrate thusobtained was immediately filtered by using a cold filtration system at−20° C., the filtered crystal was washed with about 3 g of petroleumether cooled at −30° C., and 5.89 g of white crystal was obtained. Thiscrystal was tris[tris(dimethylamino)phosphoranylidenamino]phosphineoxide with purity 98.2 weight %; however, the yield was only 20.0% andthe concentration of chlorine ion was as high as 640 ppm.

As described above, even though recrystallization was carried out usinga small amount of solvent, an extremely low temperature was required;and moreover, the yield of crystal was very low.

Comparative Example 7

The reaction was carried out exactly in the same manner as comparativeexample 5, except that the amount of iminotris(dimethylamino)phosphoraneused was 57.9 g (325 mmol) and the reaction time at the refluxtemperature of the liquid reaction product (about 40° C.) was 30 hours.And the purification was carried out at −20° C. exactly in the samemanner as comparative example 6. The mole ratio ofiminotris(dimethylamino)phosphorane to phosphorus oxytrichloride was 6.5(in excess of that stoichiometrically required). The yield after thereaction was 75.3%, and apparently the reaction rate was increasedcompared with the result of comparative example 5 only because theamount of the above described. phosphorane used was increased.

After the recrystallization, 6.57 g of white crystal was obtained. Thepurity of the crystal was 94.1 weight % and the yield was 20.7%. Evenafter the operation of recrystallization, the purity was notsatisfactory. In the crystal, about 2 weight % ofiminotris(dimethylamino)phosphorane as well as unknown impurities wasobserved. The above described phosphorane used in excess of thatstoichiometrically required in the reaction could not be fully removedby this process, as a result, it remained in the object crystaldeposited after the operation of recrystallization.

Comparative Example 8

The reaction was carried out exactly in the same manner as comparativeexample 5, except that the reaction time at the reflux temperature ofthe liquid reaction product (about 40° C.) was 40 hours. The yield afterthe reaction was 70.2%. The white slurry of petroleum ether obtained wasfiltered, and the solid was washed twice with 50 ml of petroleum ether.To the filtrate and washings obtained, water 0.12 times as heavy as thefiltrate was added, and water-washing was conducted of the filtrate andwashings while intensely shaking the mixed solution so that both of thepetroleum ether phase and the water phase were satisfactorily contactedwith each other, then the mixed solution was allowed to stand still toseparate the petroleum ether phase and the water phase from each other,and each phase was collected as a sample. This water-washing operationwas carried out another two times.

When a quantitative analysis was conducted of the petroleum ether phaseobtained, it was revealed that almost no object compound, that is,tris[tris-(dimethylamino)phosphoranylidenamino]phosphine was containedin the petroleum ether phase. Then, the same analysis was conducted ofthe water phase. The analysis revealed that 99 weight % of the objectcompound contained before water washing, together with by-products andiminotris(dimethylamino)phosphorane left unreacted, was contained in thewater phase.

EXAMPLE 9

The reaction and the water washing were carried out in the same manneras example 8, except that dried toluene was used instead ofo-dichlorobenzene. The toluene phase obtained after the water washingwas concentrated to dry at 60° C., 50 mmHg. The solid obtained was theobject compound with purity 93.5 weight %, and its yield was 82.9%.

EXAMPLE 10

The reaction and the water washing were carried out in the same manneras example 8, except that dried 2,4-dichlorotoluene was used instead ofo-dichlorobenzene. The 2,4-dichlorotoluene phase obtained after thewater washing was concentrated to dry at 90° C., 10 mmHg. The solidobtained was the object compound with purity 96.1 weight %, and itsyield was 82.4%.

EXAMPLE 11

The reaction and the water washing were carried out in the same manneras example 8, except that dried chlorobenzene was used instead ofo-dichlorobenzene, that the amount ofiminotris(dimethylamino)phosphorane used was 112 g (628 mmol), of thatthe bulk temperature at the time of dropping the above describedphosphorane was controlled to be kept at 60° C. or lower and that thereaction temperature after the dropping was 60° C. The mole ratio ofiminotris(dimethylamino)phosphorane to phosphorus oxytrichloride was6.3. The chlorobenzene phase obtained after the water washing wasconcentrated to dry at 80° C., 60 mmHg. The solid obtained was theobject compound with purity 94.1 weight %, and its yield was 67.3%.

EXAMPLE 12

The reaction and the water washing were carried out in the same manneras example 11, except that the amount ofiminotris(dimethylamino)phosphorane used was 120 g (673 mmol). The moleratio of iminotris(dimethylamino)phosphorane to phosphorusoxytrichloride was 6.7. The solid obtained by concentrating to dry thechlorobenzene phase after the water washing was the object compound withpurity 95.9 weight %, and its yield was 80.7%.

EXAMPLES 13, 14

The solid obtained by concentrating to dry o-dichlorobenzene phase,which was obtained by carrying out the reaction and the water washingexactly in the same manner as example 8, was purified in the same manneras example 8, except that normal heptane 15 times as heavy as normalhexane used in example 8 (example 13) and normal octane twice as heavyas normal hexane used in example 8 (example 14) were used. The yields ofthe object compound obtained were 83%, almost the same in both cases,and the purities were 98.9 weight % and 97.6 weight % in the orderdescribed above.

EXAMPLE 15

The reaction and the water washing were carried out exactly in the samemanner as example 8, except that the amount of the water used at a timewas 0.20 times as heavy as the filtrate and washings. The solid obtainedby concentrating to dry o-dichlorobenzene phase after the water washingwas the object compound with purity 96.5 weight %, and its yield was79.9%.

As described above, according to the present invention, in the processfor preparing phosphine oxides having the formula (2) which comprisesreacting iminophosphoranes having the formula (1) with phosphorusoxytrichloride, purification can be carried out in a simpler and easierway, the above described phosphoranes can be used in excess of thatstoichiometrically required, and the above described phosphine oxidescan be obtained with higher purity and in a higher yield in anindustrially more realistic way.

What is claimed is:
 1. A process for purifying phosphine oxides havingthe formula (2) which comprises water washing a solution containing atleast said phosphine oxides and an organic solvent substantiallyimmiscible with water to give a purified solution of said phosphineoxides, and optionally further comprising concentrating said solution todryness to give solid phosphine oxides, wherein formula (2) is asfollows:

wherein R represents the same kind or different kinds of hydrocarbongroup(s) with 1 to 10 carbon atoms, and two Rs on the same nitrogen atomcan combine with each other to form a ring structure.
 2. The process forpurifying phosphine oxides according to claim 1, wherein R of saidphosphine oxides having the formula (2) is a methyl group.
 3. Theprocess for purifying phosphine oxides according to claim 1 wherein saidorganic solvent substantially immiscible with water is an aproticorganic solvent with permittivity 2.2 or more at 20° C. which does notdissolve aminophosphonium chlorides having the formula (3)

wherein R represents the same kind or different kinds of hydrocarbongroup(s) with 1 to 10 carbon atoms, and two Rs on the same nitrogen atomcan combine with each other to form a ring structure.
 4. The process forpurifying phosphine oxides according to claim 1, wherein said phosphineoxide-containing solution is obtained by removing solid aminophosphoniumchlorides having the formula (3) from a reaction mixture containingphosphine oxides having the formula (2) and the aminophosphoniumchlorides by a solid-liquid separation process, wherein the reactionmixture is formed by reacting iminophosphoranes having the formula (1)

wherein R represents the same kind or different kinds of hydrocarbongroup(s) with 1 to 10 carbon atoms, and two Rs on the same nitrogen atomcan combine with each other to form a ring structure; with phosphorusoxytrichloride using as a reaction solvent an aprotic organic solventwith permittivity 2.2 or more at 20° C. which is substantiallyimmiscible with water and does not dissolve the aminophosphoniumchlorides having the formula (3).
 5. The process for purifying phosphineoxides according to claim 4, wherein the number of moles of saidiminophosphoranes having the formula (1) which are used per 1 mole ofphosphorus oxytrichloride is in the range of 6 to
 10. 6. The process forpurifying phosphine oxides according to claim 5, wherein the phosphineoxides containing solution is subjected to a water washing step,concentrated to dryness, and the resulting solid mixed with a saturatedaliphatic hydrocarbon and the solid left undissolved is removed by asolid-liquid separation process and purified phosphine oxide isrecovered from the saturated aliphatic hydrocarbon solution.
 7. Theprocess for purifying phosphine oxides according to claim 1, whereinsaid organic solvent substantially immiscible with water is an aproticorganic solvent with permittivity 2.2 or more at 20° C. which does notdissolve aminophosphonium chlorides having the formula (3)

wherein R represents the same kind or different kinds of hydrocarbongroup(s) with 1 to 10 carbon atoms, and two Rs on the same nitrogen atomcan combine with each other to form a ring structure.
 8. The process forpurifying phosphine oxides according to claim 1, wherein said solutioncontaining at least phosphine oxides having the formula (2) and anorganic solvent substantially immiscible with water is a solutionobtained by removing solid aminophosphonium chlorides having the formula(3) from a reaction mixture containing phosphine oxides having theformula (2) and the above described aminophosphonium chlorides by asolid-liquid separation process, wherein the liquid reaction product isformed by reacting iminophosphoranes having the formula (1)

wherein R represents the same kind or different kinds of hydrocarbongroup(s) with 1 to 10 carbon atoms, and two Rs on the same nitrogen atomcan combine with each other to form a ring structure; with phosphorusoxytrichloride using as a reaction solvent an aprotic organic solventwith permittivity 2.2 or more at 20° C. which is substantiallyimmiscible with water and does not dissolve the aminophosphoniumchlorides of formula (3):

wherein R represents the same kind or different kinds of hydrocarbongroup(s) with 1 to 10 carbon atoms, and two Rs on the same nitrogen atomcan combine with each other to form a ring structure.
 9. The process forpurifying phosphine oxides according to claim 8, wherein the number ofmoles of said iminophosphoranes having the formula (1) which are usedper 1 mole of phosphorus oxytrichloride is in the range of 6 to 10wherein formula (1) is as follows:

wherein R represents the same kind or different kinds of hydrocarbongroup(s) with 1 to 10 carbon atoms, and two Rs on the same nitrogen atomcan combine with each other to form a ring structure.
 10. The processfor purifying phosphine oxides according to claim 9, wherein thephosphine oxides containing solution is subjected to a water washingstep, concentrated to dryness, and the resulting solids are mixed with asaturated aliphatic hydrocarbon, and the solid left undissolved isremoved by a solid-liquid separation process, and purified phosphineoxide is recovered from the saturated aliphatic hydrocarbon solution.11. The process for purifying phosphine oxides according to claim 8,wherein the phosphine oxides containing solution is subjected to a waterwashing step, concentrated to dryness, and the resulting solids aremixed with a saturated aliphatic hydrocarbon, and the solid leftundissolved is removed by a solid-liquid separation process, andpurified phosphine oxide is recovered from the saturated aliphatichydrocarbon solution.
 12. The process for purifying phosphine oxidesaccording to claim 7, wherein the phosphine oxides containing solutionis subjected to a water washing step, concentrated to dryness, and theresulting solids are mixed with a saturated aliphatic hydrocarbon, andthe solid left undissolved is removed by a solid-liquid separationprocess, and purified phosphine oxide is recovered from the saturatedaliphatic hydrocarbon solution.
 13. The process for purifying phosphineoxides according to claim 4, wherein the phosphine oxides containingsolution is subjected to a water washing step, concentrated to dryness,and the resulting solids are mixed with a saturated aliphatichydrocarbon, and the solid left undissolved is removed by a solid-liquidseparation process, and purified phosphine oxide is recovered from thesaturated aliphatic hydrocarbon solution.
 14. The process for purifyingphosphine oxides according to claim 3, wherein the phosphine oxidescontaining solution is subjected to a water washing step, concentratedto dryness, and the resulting solids are mixed with a saturatedaliphatic hydrocarbon, and the solid left undissolved is removed by asolid-liquid separation process, and purified phosphine oxide isrecovered from the saturated aliphatic hydrocarbon solution.
 15. Theprocess for purifying phosphine oxides according to claim 2, wherein thephosphine oxides containing solution is subjected to a water washingstep, concentrated to dryness, and the resulting solids are mixed with asaturated aliphatic hydrocarbon, and the solid left undissolved isremoved by a solid-liquid separation process, and purified phosphineoxide is recovered from the saturated aliphatic hydrocarbon solution.16. The process for purifying phosphine oxides according to claim 6,wherein the phosphine oxides containing solution is subjected to a waterwashing step, concentrated to dryness, and the resulting solids aremixed with a saturated aliphatic hydrocarbon, and the solid leftundissolved is removed by a solid-liquid separation process, andpurified phosphine oxide is recovered from the saturated aliphatichydrocarbon solution.